Preheat oven to 425 degrees.,Generously season pork tenderloin with salt and pepper.,Heat 2 tablespoons olive oil and 2 tablespoons butter in a heavy, oven-proof skillet over high heat.,Sear tenderloin on all sides, using tongs to move it around.,______,Set pork on a cutting board to rest.,In a separate skillet, heat 1 tablespoon olive oil and 1 tablespoon butter over medium heat.,Add onion and cook for a minute, then pour in wine (if using) and chicken broth.,Add rosemary.,Stir together, then add cranberry sauce.,Heat mixture over medium heat and cook for two or three minutes.,Add more chicken broth to achieve desired consistency.,Check seasoning and add more salt or pepper if needed.,Slice pork loin and place on a platter.,Spoon cranberry sauce over the top.,Serve with mashed potatoes.